1. Field of the Invention
The present invention is related to a dustproof structure for a sleeve bearing. More particularly, the present invention is related to the dustproof structure having a dustproof cushion attached to the oil-impregnated sleeve bearing to thereby prevent from dust precipitation.
2. Description of the Related Art
Referring to FIG. 1, a conventional bearing structure for a motor consists of an axial seat 10, a motor stator 20, a motor rotor 30. The axial seat 10 is combined with an axial tube 11 in which to accommodate a sleeve bearing 12, and on which to couple the motor stator 20. In assembling, a shaft 31 of the motor rotor 30 extends through an axial hole 120 of the sleeve bearing 12 so that the motor rotor 30 is rotatably connected to the axial seat 10. Generally, lubricant contained in the sleeve bearing 12 may be driven due to rotation of the shaft 31. The lubricant successively flows through an inner circumference of the axial hole 120, an end surface of the sleeve bearing 12, an inclined surface 121 of the sleeve bearing 12, and a gap between the axial tube 11 and the sleeve bearing 12. Finally, the lubricant returns to the inside of the sleeve bearing 12. Thus, the lubricant contained in the sleeve bearing 12 is automatically circulated to lubricate the inner circumference of the axial hole 120 so as to attenuate abrasion of the axial hole 120 caused by rotation of the shaft 31. Consequently, it reduces rotational noise and prolongs useful life of the bearing.
Generally, there exists a wide clearance A between a shaft seat 32 of the rotor 30 and the sleeve bearing 12. Although the lubricant of the sleeve bearing 12 is able to attenuate abrasion, discharging the lubricant from the axial tube 11 is unavoidable while operating. Foreign dust may enter the inside of the sleeve bearing 12 and the gap between the axial tube 11 and the sleeve bearing 12. Thus, it results in precipitation of the foreign dust on the sleeve bearing 12 and the gap between the axial tube 11 and the sleeve bearing 12 that produces greasy dirt 90. Circulating the lubricant on the sleeve bearing 12, the greasy dirt 90 is collected or precipitated in a space formed on the inclined surface 121 of the sleeve bearing 12. Once the greasy dirt 90 enters the gap between the axial tube 11 and the sleeve bearing 12, the circulation of the lubricant can be obstructed. Thus, the lubricant cannot flow freely through between the axial tube 11 and the sleeve bearing 12 and it results in an insufficiency of the lubricant between the axial hole 120 and the shaft 31. The rotational speed of the motor is reduced and the running temperature of the motor is increased. Consequently, the shaft 31 of the motor may be jammed and the useful life of the motor is shortened. Hence, there is a need for an improvement of the conventional bearing structure.
To this end, U.S. Pat. No. 6,336,745, titled “OIL-IMPREGNATED BEARING AND ROTOR SHAFT,” and U.S. Pat. No. 6,435,722, titled “COMBINATION STRUCTURE FOR OIL-IMPREGNATED BEARING,” discloses a conventional bearing structure including an axial seat, a motor stator, a motor rotor, an axial tube and an oil-impregnated bearing. The bearing structure further includes a cap disposed on an end surface of the oil-impregnated bearing, and a shaft of the motor rotor includes a cushion ring arranged between the cap and the oil-impregnated bearing. In rotational operation, the cap and the cushion ring are commonly used to prevent leaking lubricant from the oil-impregnated bearing, and entering dust into the oil-impregnated bearing. However, the combination of the cap, the cushion ring and the oil-impregnated bearing is complicated that results in a disadvantage of assembling motor's members. It is important to note that an axial hole of the cap has a diameter significantly greater than an outer diameter of a shaft seat of the motor rotor. If an axial length of the sleeve bearing is relatively short, a clearance between the sleeve bearing and the shaft seat is enlarged. In use, it is inevitable that lubricant leaks out from the oil-impregnated bearing and foreign dust may enter into the oil-impregnated bearing through the cap. Thus, it results in an insufficiency of the lubricant between the axial hole and the shaft. The rotational speed of the motor is reduced and the running temperature of the motor is increased. Consequently, the shaft of the motor may be jammed and the useful life of the motor is shortened. Hence, there is a need for an improvement of the conventional bearing structure.
The present invention intends to provide a dustproof structure for a sleeve bearing which includes an axial tube in which to tightly mount a sleeve bearing and a dustproof cushion. The dustproof cushion is provided with an axial thickness to compensate a clearance between the sleeve bearing and a shaft seat so that a single (one-size) length of the sleeve bearing is suitable for various axial lengths of the axial tube. Furthermore, the dustproof cushion bears an axial hole having a diameter smaller than an outer diameter of the shaft seat to minimize a clearance between the dustproof cushion and the shaft seat. The compensating axial thickness of the dustproof cushion is applied to adjust the clearance between the sleeve bearing and a shaft seat in such a way to mitigate and overcome the above problem.